Method for vacuum tube rejuvenation



Feb. 26, 1957 J. J. SCHAEDLER :zrm. METHOD FOR VACUUM TUBE REJUVENATiON Filed Jul 6, 1953 United States Patent METHOD FOR VACUUM TUBE REJUVENATION John J. Schaedler and Dwayn A. Shipps, Kansas City, Mo.

Application July 6, 1953, Serial No. 366,106

2 Claims. (Cl. 316-2) This invention relates to vacuum tube rejuvenation, and has for its primary purpose the provision of an improved method and apparatus for restoring old and defective vacuum tubes to usefulness by the removal of inter-element shorts therefrom and the reactivation of the cathode thereof to a level of emission capabilities satisfactory for efficient operation of the tube.

Previous methods of vacuum tube rejuvenation and the apparatuses therefor have all been subject to serious limitations and disadvantages, notably the inconsistency of results obtained therewith, as well as the markedly temporary nature of the restoration obtained even with tubes whose treatment initially appeared successful.

Accordingly, it is the most important object of this invention to provide a method and apparatus for vacuum tube rejuvenation which overcomes such limitations and disadvantages experienced with prior methods and apparatuses and is adapted for successfully restoring almost all of the previously untreated tubes subjected to the method to usefulness for a reasonable period following such treatment, thereby materially extending the operating life of the tube. 7

Another important object of this invention isto provide a method of vacuum tube rejuvenation whose practice will not result in d'amageto, or adverse changes .in the operating characteristics of, the tube.

Another important object of this invention is to'pro- -vide' a method of vacuum tube rejuvenation particularly adapted for use with cathode ray and television type .tub'e's.

Another important object of'this-invention is to pro- *vide simple inexpensive and fool-proof apparatus particularly adapted-for use in practicing the method :of :the invention.

Still other important objects-of this invention will hecome clear or 'be made apparent-as the following'speci- .fication progresses.

The single-figure or thedrawing is a schematic wiring diagram of a preferred form of apparatus for practicing the method of this invention.

The most common reasons for failure of vacuum tubes as 'aresult of ordinary use'areinter-element'shorts and lowered cathode emission capabilities. As a tube is used, the active coating "on the cathode thereof is gradually rendered less and less active-the cathode being the only part of thetube that-actually wears out. "This effect is believed-to be due to the gradualexpenditrue by. the cathode of its active coating 'material1 by blowing off minute particles of same during periods of emission and the gradual building up on the cathode of a thin outer film of a relatively inactive material in covering relationship to -the-:mo re active portion of the coating, which film prevents the remaining active portion of 'the cathode-from effectively emitting the number cf -electrons required for satisfactory operation of the tube.

It is 'thes'e occurrences that 'alsocause the great majority of inter-element short-s, it being'noted that many Z,,783 ,1 1'6 Patented Feb. 26,

tances of only a few thousandths of an inch when cold,

and often by only one or two thousandths when heated, it is clear that the gradual building up. of p rtis e l 0 expended cathode material between elements, particularly between the cathode and the first or control grid adjacent thereto in view of the concurrent formation on the cathode of the above-mentioned film, will eventually result in inter-element shorts in a large number of cases. Prior attempts at vacuum tube rejuvenation by efforts to overcome the. effects of such conditions have resulted either in damaging the tube in other respects and .chang ing its operating"characteristics or in only partial rejuvenation of limited effectiveness for periods too short to justify the time and expense involved in treating the tube. The majority, if not all, of such previous methds have involved applying to the filament of the tube,f or some considerable period of time, a voltage ubstantially in excess of the characteristic or normal voltage at which the tube is designed to operate and is customarily operated in conventional applications, the purpose of thi being to superheat the coating of material on the cathode to break up the outer film of relatively inactive material formed thereon. This type .of treatment results however, in major surface irregularities and cracks in the cathode coating, with consequent dead spots in the emission pattern of the cathode, as Well as in unduly shortening the ultimate possible useful life of the tube. In the case of cathode ray and television 'tuhes particularly, such dead spots are intolerable for satisfactory performauce. v i

The method of this invention overcomes .such shortcomings of previous processes by uniformly removing or blowing off the objectionable outer film on the cathode in a manner that leaves the underlying active portion of the cathode coating exposedand in condition for further useful service in its function as an emitter of a substantially uniform pattern .of electrons, without damaging the tube or. changing itscha is concerned with the restoration of the cathode capabilitie of the tube is not elfective in the pre H pre-existin'g inter-element shorts, the method :hereof necessarily contemplates the elimination of .such ts. Further, since the removal of the objectionable inactive film from the cathode involves the liberation within the tube of minute particles of cathode material, iriterelectrode shorts are occasionally caused by the cathode emission restoration itself, which necessitates the inclusion in, the overall treatment of steps to remove such shorts after cathode restoration. I

It will be understood that any of the conventional methods and means for testing the tube to betreated for shorts and cathode emission capabilities before, during and after treatment may be employed in connection with the method of tube rejuvenation contemplated by this invention.

Referring now, more specifically, to. the steps included in our method, the first step is to apply to the filament of the tube a voltage and current equal to that characteristic voltage and current at which it is normally. operated, that is, the standard operating voltage and current recommended by the manufacturer of the tubeas. being the proper values when the tube is used in the app atially exceeded. It is likewise important that, whenever possible, although not necessarily, the tube being treated be disposed vertically with its base downwardmost, in order that the tube elements will be vertical with their open ends at the bottom to permit the escape from between elements of materials loosened from the elements during the ,burning out of shorts and the removal of the inactive cathode film.

Then, assuming that a short has been determined to exist between some adjacent pair of elements of the tube, a high voltage, direct current potential, preferably in the range of from 350 to 800 volts, is applied between the shorted elements for a period of preferably from one to five seconds, depending upon the seriousness of the short to be burned out." It has been found that, if a potential having a minimum of ripple is used for this purpose, such as filtered, fullwave rectified direct current, the necessary time of application and the chances of sparking between non-shorted tube elements are minimized. It has been further discovered that, although potentials down to slightly above 100 volts will burn out certain shorts if applied for a sufiicient length of time, the higher voltages are to be preferred for quicker action and more complete removal of the material causing the short, around 400 volts being satisfactory for eliminating most shorts, although potentials above about 650 volts and sometimes as high as about 800 volts are required for the more serious cases. It may be noted that such potential may, if desired, conveniently be simultaneously applied between each pair of adjacent elements of the tube either to burn out more than one short at a time or to prevent any possibility of the formation of a new short between one pair of elements as a result of dislodging materials theretofore causing a short between another pair of elements. In any event, it is important in this step that the potential be so applied that the cathode is at a positive potential with respect to the first or control grid, in order to prevent excessive electron emission by the cathode as a resultof undesirable conduction in the tube between non-shorted elements. It will be apparent that, if no short exists in the tube, this step may be omitted.

Next,:assuming that conventional testing has revealed that the emission capabilities of the cathode of the tube are below the acceptable level for good performance, a

highvoltage alternating current potential, preferably in the range of 700 to 900 volts, is applied between the cathode of the tube and the first or control grid of the tube, with the cathode being grounded to prevent a discharge between the cathode and filament of the tube, for a period of preferably between A and of a second, depending upon the seriousness of the cathode emission deficiency. Normally, the application of one such pulse, particularly if for a period approaching the preferred maximum limit of about of a second, is suthcient to restore the cathode emission capabilities of the tube to normal new-tube levels. In a few rare cases, repetition of this step a second or third time may be necessary and such is, of course, contemplated, although seldom required. It may be noted that application of the alternating current pulse in the manner of this step is attended by a visible discharge internally of the tube and having the general appearancecharacteristic of space discharges Y of electricity in evacuated containers. Such discharge is attended by momentary, extremely heavy electron emission by the cathode with the result that the outer, inactive film on the cathode is elfectively and substantially uniformly blown off, but without damage to the inner, active portion of the cathode coating which is thereby exposed. It is essential to this method that the potential used be at least in excess of about 500 volts and that the maximum length of the applied pulse in no event exceed one second, the shorter pulse lengths men tioned above being strongly preferred since longer pulses with the order of potential used can seriously damage the tube and virtually disintegrate the cathode coating thereof.

make available rippl efree,- :dircct Finally, in the event that the cathode emission restoration shall have caused one or more inter-electrode shorts in the tube, the short burn out step described above is repeated in the same manner. It is notable that such shorts as are caused by cathode restoration are comparatively rare, particularly when the tube is positioned with its elements disposed vertically and the open ends thereof facing downwardly during the restoration step, and, in any event, are seldom serious or difficult to eliminate by the method of this invention.

Referring now to the apparatus shown in the drawing, the numeral 16 represents a transformer having a primary winding 12 adapted for connection to a source of alternating current line voltage, a high voltage secondary winding 14 provided with a center tap 16, a rectifier filament secondary winding 18, and a filament voltage secondary winding 20 adapted for heating the filament of a tube to be treated. It will become apparent to those skilled in the art that separate transformers having secondaries equivalent to windings 14, 18 and 20 could be used, and further, that, where tubes having differing filament voltage requirements are to be treated, additional transformers or additional filaments 20 on transformer 10 could be provided together with suitable switching means for supplying the proper filament voltage to each type of tube to be treated.

A double pole, double throw switch 22 is provided, having a pole member 30 adapted to alternately engage a contact 32 and a contact 34 and a pole member 36 adapted to alternately engage a contact 38 and a contact 40, members 30 and 36 being preferably ganged, as shown, for simultaneous respective engagement with either contacts 32 and 38 or contacts 34 and 40. Winding 14 has end terminals 42 and 44, which are respectively coupled with pole members 30 and 36 by conductors 102 and 104, the center tap 16 of winding 14 being grounded through conductor 114.

A full-wave rectifier tube 46 provided with a filament 48 and a pair of plates 50 and 52 has its filament 48 coupled with winding 18 by conductors 106 and 108 and its plates 50 and 52 respectively coupled with contacts 34 and 40 of switch 22 by conductors and 112. It is thus apparent that, when pole members 30 and 36 are in a position respectively engaging contacts 34 and 40, the electrical output of winding 14 is applied to plates 50 and 52 of tube 46, center tap 16 being grounded, and a full wave rectified, direct current potential with respect to ground is made available at conductor 108.

The rectified, direct current output from conductor 108 is coupled by a conductor 116 with a filtering and voltage dividing circuit 54, which includes an input filtering capacitance 56, a resistance 58 forming a part of the filtering network and also serving as a series resistance for limiting the power drawn from tube 46, a second filtering capacitance 60 and a voltage dividing, load re sistance 62 having an intermediate tap 64. Conductor 116is connected in conventional manner with capacitance 56 and resistance 58, resistance 58 being in turn coupled with capacitance 60 and voltage dividing resist ance 62, capacitors 56 and 60 being grounded through conductor 118 and resistance 62 being grounded through conductor 120. Thus, a full wave rectified and filtered direct current potential of relatively high voltage is made available at the point of connection 66 between resistances 58 and 62, and a similar potential of somewhat less .124 with tap 64, and member 70 being coupled with a conductor 126. Obviously, resistance 62 and switch 68 could be replaced by a potentiometer, if desired,to current potentials of more than two values.

gees-sis There is as ea" "eman te gunner 32 at switqh 2;, but contact 38 is connected with a centimeter 128-. Thus, because of the grounding of center'tap 16 of Winding 14, an alternating current voltage of high potential with respect to ground is made available at conductor 128.

Manifestly, different types of power supply and filtering circuits and components from those shown could be itsed to produce the various direct and alternating current potentials required for the practice of the method of this invention. The virtue of the circuits illustrated, however,'like the entire apparatus of this invention, lies in various details of construction resulting in an effic'iently operating piece of equipment which may be manufactured with readily available and inexpensive components.

Suitable values for the various components will be obvious to those skilled in the art and need not be herein given. It may be noted, however, that the winding 14 should be capable of delivering voltage of sufiicient level for use in practicing the method hereof with the preferred values of potential described above.

A normally open switch 80 is coupled with conductor 126, and a similar switch 82 is coupled with conductor 128, switches 80 and 82 being of a quick acting type and preferably, from the standpoint of economy, although not necessarily, manually operable. Conventional types of button operated, micro-switches capable of making and breaking a circuit in of a second or less have been found well adapted for service as switches 80 and 82, it being understood that such micro-switches may be satisfactorily momentarily closed for an extremely short interval by a quick touch of the operators finger and immediately reopened by the action of the switch itself, or the switch may be operated by other means for more accurate timing of its period of closure or may even be replaced by a timed switching mechanism, if desired.

A tube receiving socket 84 is provided for receiving a tube to be treated, socket 84 preferably being supported by any suitable means (not shown) in a position adapted for supporting the tube being treated withits elements in vertical disposition with their open ends downwardmost. Socket 84 has a plurality of terminals 86, 88, 90, 92, 94 and 96 respectively adapted for connection with one filament pin or lead, the other filament pin, the cathode pin, the first or control grid pin, the second or accelerator grid pin and the anode or plate pin of a tube placed in the socket for treatment in accordance with the method of this invention. Other sockets to accommodate tubes having different pin connections could obviously be supplied and have their terminals coupled in parallel with the terminals 86-96 inclusive of socket 84.

An auxiliary socket 98 is provided having a number of terminals 150 coupled in parallel with the corresponding terminals of socket 84 by means of an elongated, flexible, multi-conductor cable 152, the individual connections being obviousfrom the drawing. Socket 150 is particularly useful for performing the method of this invention upon television tubes without removing the same from the cabinet of the television receiver.

A multi-poie, double throw switch 154 is provided with four ganged poles 156, 158, 160 and 162, pole 156 having a pair of contacts 164 and 166 associated therewith, pole 158 having contacts 168 and 170, pole 160 having contacts 172 and 174, and pole 162 having contacts 176 and 178. It will hereinafter become obvious that switch 22 could be ganged with switch 154, if desired, but is herein illustrated as separate therefrom since such latter construction has been found slightly less expensive and to permit a more compact construction with little sacrifice in convenience. It will also be appreciated that suitable testing circuits may be integrated with the apparatus of this invention by the provision of additional contacts on switches 22 and 154.

Switch 82 is coupled with contact 168 of switch 154 bye eonaueter 1'30. Switch so coupled with earnest "174 of switch 154 by conductors 13 2 and 1 34, and with the second or accelerator grid terminal 940i socket 84 by conductors 132 and 136. Contacts 164 and 1760f switch 154 have no connections, and contacts 166, 170, 172 and 178 are grounded.

Pole 1 56 of switch 154 is coupled with the anode or plate terminal 96 of socket 84 by conductors 137 and 1'38, pole 158 is coupled with the first or control grid terminal 92 by conductors 139 and 140, pole 160 is coupled with the cathode terminal 90 by conductors 141 and 142, and pole 162 is coupled with one filament terminal 86 by conductors 143, 144 and 145. Firemen-minding 20 is coupled with filament terminal 86 by conductors 146, 144 and 145, and with filament terminal 88 by conductors 147 and 148.

The operation of the above-described apparatus, when used in the practice of the method of this invention, should now be clear. It may be summarized as follows:

The primary winding 12 of the transformer 10 is coupled to a source of alternating current voltage. Switch 22 is shifted to place pole member 36 in engagement with contact 38 and switch 154 is shifted to place pole 160 in engagement with contact 172. The switch 82 is then operated for the required length of time to close the high voltage, alternating current circuit traceable from ground, through conductor 114, center tap 16 of secondary winding 14, a portion of winding 14, terminal 42, conductor 102, member 36 of switch 22, contact 38, conductor 128, switch 82, conductor 130, contact 168 of switch 154, pole 158, and conductors 139 and 140 to the first or control grid terminal 92 of socket 84, thence internally of the tube being treated to the cathode terminal 90 of socket 84, through conductors 142 and 141, pole 160 and contact 172 to ground. A high voltage, alternating current pulse of the desired potential is thereby applied between the cathode and the first or control grid of the tube being treated.

The switch 22 is then shifted to place member 36 in engagement with contact 40 and member 30 in engagement with contact 34, and switch 154 is shifted to place pole 156 in engagement with contact 166, pole 158 in engagement with pole 170, pole 160 in engagement with pole 174, and pole 162 in engagement with contact 178. Switch 68 is operated to place its pole 70 in engagement with the desired contact 72 or 74 thereof. Switch is then closed for an appropriate period to impose a high voltage, ripple-free, direct current potential upon the cathode terminal and the second or accelerator grid terminal 94 of socket 84 while the filament terminal 86, the first or control grid terminal 92 and the anode terminal 96 of socket 84 are each grounded. The circuit supplying the positive potential to the cathode terminal 90 may be traced from the secondary winding 14 of transformer 10, through conductors 102 and 104 to poles 30 and 36 of switch 22, thence through contacts 34 and 40 and conductors and 112 to the plates 50 and 52 of the rectifier tube 46, then from the filament 48 of tube 46 through conductor 116, filter and voltage divider 54, switch 68, conductor 126, switch 80, conductors 132 and 134, contact 174 of switch 54, pole and conductors 141 and 142 to the cathode terminal 90.

If required, switch 82 may again be closed with switches 22 and 154 in their first above described positions to repeat the short burn out step of the method.

It'will be appreciated that many changes and modifications might be made in the method and apparatus of this invention without materially departing from the spirit thereof. Accordingly, we desire to be limited only by the scope of the appended claims.

Having thus described the invention what is claimed as new and desired to be secured by Letters Patent is:

l. A method for rejuvenating an old and defective vacuum tube of the kind provided with a number of elements including a grid, a cathode and a filament having a characteristic operating voltage, said method including the steps of applying across the filament of the tube an electrical potential equal to its characteristic operating voltage, whereby to heat the cathode of the tube to its normal operating temperature; and thereupon, applying an alternating current potential in excess of five hundred volts between thecathode of the tube and the grid of the tube for a period of less than one second with the cathode of the tube grounded, whereby to increase the electron emission capabilities of the cathode of the tube.

2. In the method as set forth in claim 1, wherein said alternating current potential is between seven hundred and nine hundred volts, and said period is between one one-hundredth and one-tenth of a second.

References Cited in the file of this patent UNITED STATES PATENTS 1,337,245 Macpherson Apr. 20, 1920 1,608,083 Daley Nov. 23, 1926 1,881,645 Jones et al. Oct. 11, 1932 2,070,435 Katzman Feb. 9, 1937 2,371,327 Hendry Mar. 13, 1945 2,413,707 Helliar Jan. 7, 1947 2,452,401 Stivin Oct. 26, 1948 2,717,190 Shoup Sept. 6, 

